I. FIELD OF THE INVENTION
This invention relates to shaped refractory products made primarily of silica or refractory metal oxides, e.g. alumina, zirconia, titania, tungsten oxide etc., and more particularly to a process of producing such shaped products.
II. DESCRIPTION OF THE PRIOR ART
Shaped refractory products made primarily of refractory oxides have a variety of uses. For example, they may be used as catalyst supports, packing materials and insulating materials. The products are preferably produced in the form of hollow spheres when used for these purposes. Hollow spheres are generally formed by coating a volatile core with a ceramic powder and then heating the coated cores to cause the ceramic powder to sinter and to cause the core to disappear by volatilization (e.g. as disclosed in Watson et al. U.S. Pat. No. 4,039,480 issued on Aug. 2, 1977 ). Another method of forming oxide spheres is disclosed in Schmitt U.S. Pat. No. 3,792,136 issued on Feb. 12, 1974. This involves impregnating resinous microspheres with a metallic compound, heating the microspheres slowly to carbonize the resin and igniting the microspheres to remove the carbon and to produce the metal oxide.
These methods are not easy to carry out and tend to be expensive and so an object of the invention is to provide an alternative procedure for forming such products.